Both of my lab classes this semester went over material and lab techniques that I have learned before (a molecular genetics course and general chemistry, I've done intense mol gen lab work and I've taken the equivalent of AP Chem, with labs, I just never took the test). By your logic, as long as I did the written work, I would have been able to skip out of those labs. Not a great example, I'll admit, but I really didn't learn much of anything new.
I've found that most syllabi I've received clearly stipulate the requirements for getting a good grade. Most of the advice in this thread to the OP has been to deal with the grade they've been given. I don't like rules that much either, whether or not that shows. I compulsively cut class in high school and I was essentially a slacker. But that doesn't mean I argued every single time when I cut class or handed in an assignment late that I deserved the higher grade if I knew I didn't deserve that bump. You're not setting the rules, you're breaking the rules set out by the professor. He's the one that's grading you, he has every right to give you the lower grade whether or not attendance is essential. It's not a democracy, the class is a dictatorship--and that's what you're paying for, whether or not the discussion section was useful.
It's great that you want to learn, but you don't always need a university or a degree to do that (unschooling, anyone?). A grade is an arbitrary measurement set out by the instructor. You have to deal. I mean, you said you're in university because you want to learn. Regardless of the grade, you learned something!